Method for processing catalysts for color number hydrogenation of polytetrahydrofuran and/or the esters thereof

ABSTRACT

Process for working up an at least partially deactivated hydrogenation catalyst for the color number hydrogenation of PTHF and/or PTHF esters, in which the hydrogenation catalyst is purified by treatment with steam at from 100 to 250° C. and a gauge pressure of from 0 to 40 bar.

The invention relates to a process for working up at least partiallydeactivated catalysts which have been used for the preparation ofpolytetrahydrofuran, polytetrahydrofuran monoesters and diesters havinga low color number by treatment with hydrogen, referred to as colornumber hydrogenation.

It is known from DE-A 31 12 065 that the treatment ofpolytetrahydrofuran (hereinafter referred to as “PTHF”) orpolytetrahydrofuran monoesters and/or diesters (hereinafter referred toas “PTHF esters”) with hydrogen in the presence of hydrogenationcatalysts leads to corresponding polymers having a low color number.Possible PTHF esters are, in particular, PTHF monoacetates, PTHFdiacetates or mixtures thereof which are obtainable by polymerization oftetrahydrofuran (hereinafter referred to as “THF”) in a manner known perse, preferably in the presence of acetic anhydride over varioushydrogenation catalysts.

In general, hydrogenation catalysts tend to lose activity andselectivity as the number of hours of operation increases. Afterreaching a limiter value which is no longer acceptable, thehydrogenation catalyst of an industrially operated color numberhydrogenation process has to be replaced by a fresh hydrogenationcatalyst having a high activity and selectivity.

The replacement of the exhausted, deactivated catalyst is generallyassociated with a purification procedure by means of which the exhaustedcatalyst is freed of adhering product, in particular PTHF and PTHFesters.

The usual procedure for the hydrogenation catalysts used for the colornumber hydrogenation is to empty the PTHF or PTHF ester from the reactorand then rinse the still product-containing catalyst in the reactor withhot water having a temperature of about 60-90° C., eitherdiscontinuously a number of times or continuously. This results in largequantities of rinsing water. The rinsing water obtained has to be workedup. Moreover, the removal of adhering impurities from the catalyst isincomplete since, for example, PTHF diacetates are insoluble in water.

As a result of the incomplete cleaning of the hydrogenation catalyst bythe rinsing with hot water, conglutination of the catalyst particles toform larger units such as granules or lumps occurs when the catalyst isremoved from the reactor by means of suction, which is usuallyassociated with cooling. The removal of the catalyst from the reactor bymeans of suction which is required in the industrial processes is madedifficult or impossible. The hydrogenation catalyst removed from thereactor is also still highly contaminated after the purificationprocedure.

As an alternative, the catalyst can be washed with solvents such asmethanol. Although this gives a free-flowing catalyst which can readilybe removed by means of suction, disadvantages are the long time of anumber of days required for this procedure and the costly work-upnecessary for the methanol used for washing.

It is an object of the present invention to provide a process forworking up exhausted catalysts which have been used for the preparationof PTHF, PTHF monoesters and/or PTHF diesters having a low color numberby treatment with hydrogen, which allows a quick and inexpensive changeof catalyst and which gives a worked-up catalyst which is largely freeof product residues and can readily be handled in subsequent disposal.

We have found that this object is achieved by a process for working upan at least partially deactivated hydrogenation catalyst for the colornumber hydrogenation of PTHF and/or PTHF diesters, in which thehydrogenation catalyst is purified by treatment with steam at atemperature of generally from 100 to 250° C., preferably from 100 to200° C., particularly preferably from 100 to 150° C., and a gaugepressure of generally from 0 to 40 bar, preferably from 1 to 16 bar,particularly preferably from 2 to 4 bar. The purified hydrogenationcatalyst for the color number hydrogenation of PTHF and/or PTHF esterscan be passed to disposal in a second step. It is preferably passed tometal recovery, but it is also possible to deposit the purifiedhydrogenation catalyst in a landfill, to regenerate it or to incinerateit.

The steam treatment purifies the hydrogenation catalysts to such anextent that the eluate obtained in the steam purification has anevaporation residue ER of ≦2%.

The process of the present invention is used for working up at leastpartially deactivated hydrogenation catalysts for the color numberhydrogenation of PTHF and/or PTHF esters, preferably PTHF monoacetatesand/or PTHF diacetates. The hydrogenation catalyst for the color numberhydrogenation is considered to be partially deactivated when it has lostits original catalytic activity and/or when the color number of thepolymer can no longer be reduced significantly by the color numberhydrogenation. A partially deactivated hydrogenation catalyst can, forexample, have a residual activity of 80% of the original activity. It ispossible to work up hydrogenation catalysts which have been used for thecolor number hydrogenation of polymers from the polymerization of THF toPTHF or from the copolymerization of THF with alkylene oxides such asethylene oxide or propylene oxide to form the correspondingpolybutylene-alkylene glycol ethers. The polymerization can also havebeen carried out as a copolymerization in the presence of telogens.Examples of telogens are water, monohydric or polyhydric alcohols suchas methanol, ethanol, propanol, ethylene glycol, butylene glycol,glycerol, neopentyl glycol, 1,4-butanediol, also aliphatic carboxylicacids having from 1 to 8 carbon atoms, e.g. formic acid, acetic acid,propionic acid, butyric acid, and aromatic carboxylic acids such asbenzoic acid and also their anhydrides.

The at least partially deactivated hydrogenation catalysts from thecolor number hydrogenation are contaminated with the products of thepolymerization or copolymerization. Products of the polymerization orcopolymerization are PTHF, polybutylene-alkylene glycol ethers or theirreaction products with the telogens mentioned, e.g. PTHF monoesters,PTHF diesters.

The process of the present invention is used for the work-up ofhydrogenation catalysts for color number hydrogenation. Suitablehydrogenation catalysts are known, for example, from DE-A 31 12 065 andcomprise metals of transition group 8, in particular nickel, cobalt,iron and also the noble metals ruthenium, palladium or platinum, alsocopper. The metals can be employed in pure form, e.g. as Raney metals oras reduced oxides. However, catalysts comprising the hydrogenationmetals on suitable supports such as aluminum oxide, silicon oxide,pumice, bentonite or, for example, magnesium silicate have also beenfound to be useful. The catalysts comprising base metals such as iron,cobalt, nickel and copper are advantageously converted into the activeform by reduction with hydrogen prior to use. When noble metal catalystsare employed, such an operation is superfluous in most cases. Theprocess of the present invention is preferably applied to hydrogenationcatalysts for color number hydrogenation which comprise nickel andcopper and are preferably supported.

To carry out the process of the present invention, the color numberhydrogenation reactor is emptied by draining off the reaction mixture.The catalyst remaining in the reactor is then treated continuously ordiscontinuously with steam, preferably from the top downward, at from100 to 250° C., preferably from 100 to 200° C., particularly preferablyfrom 100 to 150° C., and a gauge pressure of from 0 to 40 bar,preferably from I to 16 bar, particularly preferably from 2 to 4 bar.

The physical stripping effect of the steam restores the free-flowingnature of the hydrogenation catalyst, so that it can be removed from thehydrogenation reactor without problems. Any catalyst beds in anyreaction apparatuses can be worked up in this way. For example, thecatalyst can be present in the form of crushed material, extrudates,spheres or other shaped bodies. The purified catalyst can, for example,be removed from the hydrogenation reactor by means of suction or bydraining it out from the bottom.

The time for which the catalyst is treated with steam is generally from2 to 100 hours, particularly preferably from 5 to 50 hours.

Condensation of the steam, either in the hydrogenation reactor orpreferably in a separate apparatus, gives an eluate (condensate)comprising water and impurities removed from the catalyst.

PTHF, PTHF monoesters or PTHF diesters present in this eluate can beseparated off by, for example, phase separation. It is also possible towork up the eluate by distillation. Furthermore, the PTHF and/or PTHFesters present can be depolymerized in a separate apparatus. Themonomers obtained by depolymerization can be recirculated. The residualcondensate which remains can be sent as wastewater to a water treatmentplant.

The hydrogenation catalyst for color number hydrogenation which has beenpurified by the process of the present invention is free of PTHF and/orPTHF esters and can, since it is fine-grained and free-flowing, beremoved from the reactor by means of suction without problems. Theprocess of the present invention makes friction-free removal of thecatalyst from the reactor possible. The deactivated hydrogenationcatalyst from color number hydrogenation of PTHF and/or PTHF esters ispreferably passed to metal recovery. It is also possible for it to bedeposited in a landfill, regenerated or incinerated.

The following examples illustrate the invention.

Color Number Hydrogenation

Tetrahydrofuran was polymerized by the continuous polymerization methoddescribed in DE-A 29 16 653 (U.S. Pat. No. 4,189,566) using bleachingearth as catalyst and acetic anhydride as regulator substance. Thepretreatment likewise described in this publication for purifyingcommercial tetrahydrofuran was omitted. The polymerization was carriedout using technical-grade tetrahydrofuran from BASF Aktiengesellschaft.A PTHF diacetate having a molecular weight of 650 was prepared asdescribed in example 3 of DE-A 29 16 653. This polymer had a colornumber of 100 APHA. The PTHF diacetate leaving the reactor was passedfrom the bottom upward over a catalyst bed comprising 3 mm silica gelextrudates containing 0.4% of palladium while introducing gaseoushydrogen. The product leaving the hydrogenation had a color number ofless than 10 APHA. The space velocity of the catalyst was 0.4 kg ofpolymer solution per liter of catalyst and hour. The amount of hydrogenintroduced per hour was 1 standard l/l of polymer solution. The polymersolution which had been treated by hydrogenation was freed of excesstetrahydrofuran and the resulting diacetate was hydrolyzed. This finallygave PTHF having a color number of about 15 APHA and an acid number of 0mg KOH/g.

EXAMPLE 1

The partially deactivated catalyst used for the above-described colornumber hydrogenation was, after a period of operation of 23 months,treated with 4 bar steam from the top downwards at 160° C. for 24 hours.The flow rate was about 1 t/h.

After 24 hours, a very free-flowing catalyst bed was obtained and thiscould be removed by means of suction without problems. The condensateobtained toward the end had TOC contents of <1%. The further analyticalvalues are shown in table 1. The corresponding values for a condensateobtained right at the beginning of the steam treatment are also shown intable 1 as example C1.

Determination of the Acid Number (AN)

The acid number is determined by means of equivalence point titrationwith potassium hydroxide (KOH). The acid number gives the amount ofpotassium hydroxide in mg which is required to neutralize 1 g of thesample.

Determination of the Evaporation Residue (ER)

The evaporation residue is the proportion of nonvolatile materialpresent in PTHF or PTHF ester/low boiler mixtures determined underprescribed conditions. To determine the ER, a sample is evaporated for60 minutes at 140° C. under atmospheric pressure and for 30 minutes atthe same temperature and a pressure of less than 1 mbar in anevaporation flask. The evaporation residue is calculated according to${ER} = \frac{m_{2} \times 100}{m_{1}}$

In this equation,

-   -   ER=Evaporation residue, mass fraction in accordance with DIN        1310 in g/100 g    -   m₁=Mass in g of the evaporation flask with the sample    -   m₂=Mass in g of the evaporation flask with the evaporation        residue    -   100=Conversion factor from g to 100 g        Determination of the THF Content

The THF content of the eluate was determined gas-chromatographically(head space gas chromatography). TABLE 1 ER AN THF Example [%] [mgKOH/g] [ppm] C1 17.4 5.7 29171 1 1.28 10.6 652

1. A process for working up an at least partially deactivatedhydrogenation catalyst for the color number hydrogenation of PTHF and/orPTHF esters, comprising purifying a hydrogenation catalyst comprisingnickel, cobalt, iron, ruthenium, palladium, platinum or copper bytreatment with steam at from 100 to 250° C. and a gauge pressure of from0 to 40 bar.
 2. A process as claimed in claim 1, wherein thehydrogenation catalyst is a supported catalyst.
 3. (canceled)
 4. Aprocess as claimed in claim 1 for working up hydrogenation catalysts forthe color number hydrogenation of PTHF monoacetate and/or PTHFdiacetate.
 5. A process as claimed in claim 2 for working uphydrogenation catalysts for the color number hydrogenation of PTHFmonoacetate and/or PTHF diacetate.